This invention relates generally to devices for the treatment of spinal conditions, and more particularly, to the treatment of various spinal conditions that cause back pain. Even more particularly, this invention relates to devices that may be placed between adjacent spinous processes to treat various spinal conditions. For example, spinal conditions that may be treated with these devices may include spinal stenosis, degenerative disc disease (DDD), disc herniations and spinal instability, among others.
The clinical syndrome of neurogenic intermittent claudication due to lumbar spinal stenosis is a frequent source of pain in the lower back and extremities, leading to impaired walking, and causing other forms of disability in the elderly. Although the incidence and prevalence of symptomatic lumbar spinal stenosis have not been established, this condition is the most frequent indication of spinal surgery in patients older than 65 years of age.
Lumbar spinal stenosis is a condition of the spine characterized by a narrowing of the lumbar spinal canal. With spinal stenosis, the spinal canal narrows and pinches the spinal cord and nerves, causing pain in the back and legs. It is estimated that approximately 5 in 10,000 people develop lumbar spinal stenosis each year. For patients who seek the aid of a physician for back pain, approximately 12%-15% are diagnosed as having lumbar spinal stenosis.
Common treatments for lumbar spinal stenosis include physical therapy (including changes in posture), medication, and occasionally surgery. Changes in posture and physical therapy may be effective in flexing the spine to decompress and enlarge the space available to the spinal cord and nerves—thus relieving pressure on pinched nerves. Medications such as NSAIDS and other anti-inflammatory medications are often used to alleviate pain, although they are not typically effective at addressing spinal compression, which is the cause of the pain.
Surgical treatments are more aggressive than medication or physical therapy, and in appropriate cases surgery may be the best way to achieve lessening of the symptoms of lumbar spinal stenosis and other spinal conditions. The principal goal of surgery to treat lumbar spinal stenosis is to decompress the central spinal canal and the neural foramina, creating more space and eliminating pressure on the spinal nerve roots. The most common surgery for treatment of lumbar spinal stenosis is direct decompression via a laminectomy and partial facetectomy. In this procedure, the patient is given a general anesthesia and an incision is made in the patient to access the spine. The lamina of one or more vertebrae may be partially or completely removed to create more space for the nerves. The success rate of decompressive laminectomy has been reported to be in excess of 65%. A significant reduction of the symptoms of lumbar spinal stenosis is also achieved in many of these cases.
The failures associated with a decompressive laminectomy may be related to postoperative iatrogenic spinal instability. To limit the effect of iatrogenic instability, fixation and fusion may also be performed in association with the decompression. In such a case, the intervertebral disc may be removed, and the adjacent vertebrae may be fused. A discectomy may also be performed to treat DDD and disc herniations. In such a case, a spinal fusion would be required to treat the resulting vertebral instability. Spinal fusion is also traditionally accepted as the standard surgical treatment for lumbar instability.
A wide variety of spinal fusion devices are used following partial or total discectomies for stabilization of the spine at that site. Many such devices are secured extradiscally, such as to the pedicles or spinous processes. For example, the spinous process fusion plate available from Medtronic, Spinal and Biologics of Memphis, Tenn. under the brand name CD Horizon Spire is typically secured to the spinous processes. See for example the devices and methods disclosed in U.S. Pat. Nos. 7,048,736 and 7,727,233, the entire contents of which are expressly incorporated herein by reference. These devices typically work for there intended purposes. However, with the demands of spinal surgery, the medical device industry is continually looking for ways to improve currently available devices.